The present invention relates to a gasket having soft and hard coatings thereon to effectively seal around a fluid hole of an engine.
In order to seal around a fluid hole, a gasket is installed between two parts. In an automobile, all the parts are subjected to heat and vibration, so that sealing at a joint portion of two parts of the automobile is liable to be damaged to cause leakage of fluid. Therefore, there has been proposed many methods to solve this problem.
One of conventional methods is that a resilient layer or soft coating with a predetermined lateral length is formed on a plate around a hole to be sealed. Since the one resilient layer is formed on the plate, when heavy pressure is repeatedly applied thereto, the resilient layer may break.
In order to improve the above drawbacks, U.S. Pat. Nos. 4,778,189 and 4,828,275 have been proposed, wherein a plurality of elastic members is formed around a hole to be sealed to spread compression force applied thereto. However, if tightening pressure is strong, the elastic members may still break or flow.
On the other hand, when a cylinder head is formed, a plurality of small scratches or grooves is formed on the surface of the cylinder head due to cutter traces. In order to fill in the small scratches, it is a conventional practice to form a soft coating on a surface of a gasket abutting against a cylinder head.
The soft coating is not so strong against high heat and pressure. Namely, if high heat and pressure is applied to the soft coating, the soft coating looses its elasticity and may creep or flow. Therefore, the soft coating can not be applied thick in a gasket, because surface pressure on the gasket gradually decreases due to creep or flow of the soft coating.
On the other hand, a hard coating does not deform so much against high heat and pressure, i.e. low permanent distortion against heat and compression. Therefore, a hard coating may be applied onto an entire surface of a gasket in case the surface of the gasket is not mechanically strong, such as a compressible material made of rubber and organic or inorganic fibers.
However, since the hard coating can not fill in small scratches on the surface of the cylinder head nor is suitable for sealing, the soft coating may be applied onto the outer surface of the hard coating if required. Also, in case the soft coating does not adhere to a gasket, the hard coating may be applied onto the gasket to operate as a primer.
Accordingly, one object of the present invention is to provide a gasket which can effectively seal around a fluid hole by utilizing hard and soft coatings.
Another object of the invention is to provide a gasket as stated above, wherein a sealing mechanism around a fluid hole can be easily and economically formed on a gasket.
Further objects and advantages of the invention will be apparent from the following description of the invention.